Depolymerization of high boiling unsaturated hydrocarbons



' Patented Ms '12, 1- 942 UNITED STATES PATENT o FIcs mamas DEPOLYMERIZATION OF HIGH BOILING UNSATURATED HYDBOCABBONS Karl Smeykal and Kurt Beisinger, Leona, Ger- 1 assignors, by.mesne assignments, to.

William E. Currie, New York, N. Y.

No Drawing. Application September 1, 1938, Se-

rial No. 227,988. InGermany September '7,

- 3 Claims. (01. zoo -cs3) The present invention relates to the depolymerization of high boiling unsaturated hydrocarbons.

to form higher molecular unsaturated hydrocarbons. The reaction products thus formed usually contain not only dimers but also considerable amounts of trimers, tetrimers and higher polymers of the olefines used. polymerized beyond the dimeric stage, however, there are not always suitable possibilities of use, so that they are frequently undesirable by-products. In order to render them valuable it has For the compounds the same'throughput of thepolymers by reason been proposed to split them up again into lower molecular oleflnes, in particular to dimers and monomers, by leading them at elevated tempera-' tures over suitable catalysts, as for example bleaching earths, such as-fullers earth or the bleaching earth known under the trade name "Tonsil." The catalysts used, however, very soon become inactive so that the depolymerization rapidly subsides. Even by slowly raising the reaction temperatures, the activity of the catalysts used cannot be retained appreciably'longer, and at the higher temperatures they readily clog up by carbon deposition.

We have now found that the catalysts used for the depolymerization of polymeric oleflnes can be kept active for very'long periods by carrying out the depolymerization in the presence of appreciable amounts of steam. For this pu p se the overpolymerized oleflnes are led advantageously in the vapor phase-together with steam at elevated temperature over the depolymerizing catalysts, the resulting products then being condensed. The steam is usually employed in amounts of more than 20 per cent and not more than 80-per cent and preferably amounts of from 40 to 60 per cent by volume with reference to the vaporized oleflne polymers. The reaction is usually carried out at atmospheric pressure, but reduced or increased pressures may be used. The reaction temperatures usually lie between 200 and 400 0.; it is preferable to work between 230 and 300 C;

As depolym'erlzing catalysts there may bementioned in particular surface-active substances, as for example bleached earths, which if desired may be subjected to a pretreatment with acids, such as hydrofluoric acid or hydrochloric acid.

As initial materials there may be mentioned in particular those oleflne polymerization products,

especially those boiling above 170 C., of which the monomeric components boil below C., as for example tri-isobutylene, tetra-isobutylene and higher polymers of isobutylene or the corresponding polymers of isohexyl'ene, and also high-v er polymers of propylene or the amylenes, hexylenes and heptylenes.

By the presence of the steam, the life of the catalysts may be prolonged without trouble to four to eight or more times that in the absence of steam.

Furthermore, in spite of the shortening of the times of contact in the catalyst chamber with of the supply of steam, there is not, aswould have been'expected, a decrease in the degree of reaction, but surprisingly there is even an increase in the same as compared with working without the steam.

Tliejsaid method of working may be used for splitting up polymers formed by processes other than the preparation of olefine dimers, for example when the compounds which have not been sufliciently polymerized in the preparation of highly polymerized compounds are-to be split up for fresh polymerization.

The following examples will further illustrate how the said invention may be carried out in practice, but the invention is not restricted to these examples. The percentages are by volume. The parts are by weight.

Example 1 Tri-isobutylene (obtained as a by-product in the preparation of di-isobutylene by the treatment of isobutylene with acids, such as phosphoric acid, sulphuric acid or other catalysts) is vaporized and mixed with steam in such amounts that a mixture of 58 per cent of tri-isobutylene vapor and 42 per cent of steamis formed. This mixture is led at 230 C. over a catalyst consisting of the bleaching earth knownunder the trade name TonsiP pressed into pieces, the throughput beingsuch that half a unit of liquid triisobutylene is used per hour for each unit of catalyst volume. The elfluent vapors .are led through a stripper, condensed in strongly cooled vesi'iszls attached thereto and then separated from 100 parts of tri-is'obutylene are thus split up 5 into 35 parts of isobutylene and 30 parts of diisobutylene. The remainder is unchanged. Aftcent of steam and 63 per cent of tetra-isobutyler 39 days, the activity of the, catalyst is retained ene, is led at 230 C. over bleaching earth known to such an extent that under the same working ,as Frankomt H, the throughput of tetra-isocondltions 100 parts oi tri-isobutylene are split butylene measured as liquid per hour being about up into 30 parts of isobutylene and 22 parts of 6 0.6 times the catalyst volume. di-isobutylene. 01"100 parts or tetra-isobutyiene, 60 parts are When working without the addition of steam,' split into 17 parts of isobutylene, 32 parts of but under otherwise identical conditions, 100 1 di-isobutylene and 11 parts of tri-isobutylene. parts of tri-isobutylene are at first split up into The remainder of the reaction product (40 parts) 18 parts of isobutylene and 29 parts of di-isois unchanged tetra-isobutylene.

butylene (the remainder being unchanged tri- What we claim is: isobutylene); but the catalyst becomes entirely 1. In the process 0! depolymerizing polymers inactive after operation for 6 days. of low boiling oleflnes by passing said oleflne Example 2 polymers at an elevated temperature over a surface active clay catalyst in which the clay it- A mixt r of b t 25 per t, of steam and a self is the efiectivecatalytic component, the imabout 74 per cent of di-isoheptylene vapor is provement which. comprises eflecting such deled over a bleachin earth known in trade as p ym a n n e pr s e 01 an app a l Frankonit H at 230 0., the hourly througham un f st am which perates on the y 1% put of di-isoheptylene measured as liquid being 20 self to, maintain the catalytic activity thereof.

about 0.6 times the catalyst volume (volume of 2. In the pro ss-as claimed in claim 1, operatthe reaction space filled by the catalyst). ing at a temperature between 200 and 400 C.

or 100 parts of di-isoheptylene, '70 parts are 3. In the process as cla med n c a m 11 split up into 49 parts of isoheptylene and 21 parts ing the po yme et r w h t e s 20 D of'a fraction boiling betweer 100 and 180 c. 25 cent by volume of steam ver th dep m r The remainder parts) of the reaction proding catalyst.

uct consistsof non-split di-isoheptylene. KARL SMEYKAL.

Example 3 .KURT REISINGER.

A vapor mixture consisting of about 37 per 30 

